Controlling spark for an engine with controllable valves

ABSTRACT

A system and method to control spark in a cylinder of a multi-cylinder engine. Spark can be controlled in a cylinder while reducing the possibility of producing a spark at a spark plug coupled to an ignition coil.

The present application is a continuation of U.S. patent applicationSer. No. 10/924,471 filed Aug. 24, 2004 now U.S. Pat. No. 7,082,934, theentire contents of each of which are incorporated herein by reference intheir entirety.

FIELD

The present description relates to a method for controlling ignitionspark in an engine having controllable valves and more particularly to amethod for controlling spark during an indication of a degraded valve.

BACKGROUND

Selectively operable valves may be used in some circumstances to improvefuel economy, emissions, and performance of a piston driven internalcombustion engine. Operation of individual valves may be based on asingle or a combination of engine operating conditions so that thenumber of operating valves can be adjusted to meet demand and controlobjectives. Several different methods may be used to selectively operateor inhibit operation of valves including: mechanically inhibited camactuated valves, electrically actuated valves, and electrohydraulicactuated valves. If valve degradation of selectively operated valves canbe determined, it may be beneficial to control ignition spark during acombustion cycle of a cylinder based on the degradation.

One method to control engine ignition spark is described in U.S. Pat.No. 6,401,684. During an abnormal valve operating condition, at thetransition from an open intake valve condition to a closed intake valvecondition, this method attempts to delay ignition spark by increasingthe duration of current flowing into the ignition coil until the secondhalf of the power stroke in the respective cylinder. In addition, themethod may attempt to inhibit ignition spark, if the ignition coil hasnot started to charge, when an abnormal valve condition is generated atthe transition from a closed intake valve condition to an open intakevalve condition. Furthermore, the method may also attempt to inhibitspark if an abnormal condition is generated at a transition from an openexhaust valve condition to a closed exhaust valve condition.

The inventors herein have recognized that the before-mentioned approachcan have several disadvantages. For example, extending coil charginginto the second half of the power stroke may produce more than adesirable amount of coil current which could degrade the ignition coil.Further, the method attempts to extend a spark event to a point that islate in the cylinder cycle. As a result, combustion may still occursince both spark and fuel can be present in the cylinder. If an intakevalve remains open during combustion, the intake manifold temperatureand pressure may increase more than desired. On the other hand, if anexhaust valve remains open during combustion, the exhaust valvetemperature may increase more than desired. As such, following theapproach taught in the prior art may lead to several issues.

SUMMARY

One embodiment of the present description includes a method ofinterrupting at least a spark event to at least a cylinder of amulti-cylinder internal combustion engine having at least a valveoperable in the cylinder, the method comprising: limiting the voltage ofan ignition coil after beginning to charge said ignition coil; and saidvoltage limited while reducing the possibility of producing a spark at aspark plug coupled to said ignition coil. This method can be used toreduce the above-mentioned limitations of the prior art approach.

By limiting the voltage of an ignition coil that delivers energy to aspark plug located in a cylinder while reducing the possibility ofproducing a spark at a spark plug it may be possible to reduce ignitioncoil degradation. Furthermore, intake manifold temperature, intakemanifold pressure, and exhaust valve temperature may be reduced whenignition coil voltage is limited during a condition of valvedegradation.

In particular, valves that may be selectively activated during a cycleof a cylinder, may experience degraded operation under certainconditions. This can include valves that may be operated without regardto crankshaft position, (e.g., electrically actuated valves, includingelectrohydraulic and electromechanical valves). If degraded valveoperation is determined, it may be beneficial to control combustion inthe affected cylinder. For example, if an intake and/or exhaust valvedoes not follow a desired trajectory, spark can be controlled, in theaffected cylinder, so that the uncombusted air-fuel mixture may not beignited by a spark from the spark plug. This may be achieved by limitingthe voltage of the ignition coil so that the voltage potential acrossthe spark plug is below the level that causes a spark. By limiting theignition coil voltage, spark in a cylinder may be controlled withoutproducing elevated ignition coil current or delayed combustion. Inaddition, via spark control, combustion can be regulated in a cylinderto reduce the temperatures and pressures that intake and/or exhaustmanifolds and valves may experience.

In another aspect of the present description, the present descriptionprovides for a system for interrupting a least a spark event to at leasta cylinder of a multi-cylinder internal combustion engine having atleast a valve that may be held in a position during a cycle of said atleast a cylinder, the system comprising: an ignition coil comprising acore, a primary winding, a secondary winding, and an auxiliary winding;and a switching device to allow current flow in said auxiliary winding.

In other words, spark delivery to a cylinder may also be inhibited bycontrolling the flow of current in an ignition coil. Active coil currentcontrol, (i.e., regulating the current flow in one or more coils of anignition coil), or passive coil current control, (i.e., shunting anauxiliary coil, for example), may be used to control the current flow inthe ignition coil secondary winding. This can reduce the inducedsecondary coil voltage, thereby decreasing the probability of creating aspark in the cylinder.

The present description can provide several advantages. For example,during a condition of valve degradation, spark may be controlled beforeor after an ignition coil has begun to charge. This may allow a singleand simple spark control strategy to regulate combustion in a cylinder.In addition, engine emissions may be reduced during conditions of valvedegradation since combustion in a cylinder experiencing valvedegradation may be regulated. For example, reducing the amount ofexhaust gas that may be pumped from a cylinder having valve degradationinto the intake manifold may reduce the probability of misfire in otherengine cylinders, thereby lowering engine emissions.

Note also that various other approaches may be taken in determining andresponding to valve degradation.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following detaileddescription of the preferred embodiments when taken alone or inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings,wherein:

FIG. 1 is a schematic diagram of an engine having selectively operableintake and exhaust valves;

FIG. 2 is a schematic diagram that shows details of an exampleelectrically actuated valve;

FIG. 3 is a flow diagram that shows an ignition coil voltage limitingstrategy;

FIG. 4 is a flow diagram that shows an alternate ignition coil voltagelimiting strategy;

FIG. 5 is an example diagram that shows a low side primary ignition coilvoltage limiting circuit;

FIG. 6 is an example diagram that shows a shunt primary ignition coilvoltage limiting circuit;

FIG. 7 is an example diagram that shows a auxiliary coil low sideconfiguration for a magnetic flux based voltage limiting circuit;

FIG. 8 is an example diagram that shows a auxiliary coil reduced wirecount shunt configuration for a magnetic flux based voltage limitingcircuit;

FIG. 9 is an example diagram that shows a auxiliary coil shuntconfiguration for a magnetic flux based voltage limiting circuit;

FIG. 10 is an example diagram that shows a auxiliary coil high sidedrive configuration with reduced wires count for a magnetic flux basedvoltage limiting circuit; and

FIG. 11 is a plot of a simulated spark interrupt event.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52, and exhaust valve 54. Intake and/or exhaustvalves may be electrically actuated, (e.g., electromechanical orelectrohydraulic), or they may be mechanically driven via a camshaft andhaving a known means for selectively activating and/or deactivating thevalves. Furthermore, combinations and sub-combinations of mechanical,electromechanical, mechanically deactivated, and electrically actuatedintake and exhaust valvetrains may be configured, but are not shown.Note: a deactivated valve may be in an open or closed state whiledeactivated.

Intake manifold 44 is shown having fuel injector 66 coupled thereto fordelivering liquid fuel in proportion to the pulse width of signal FPWfrom controller 12. Fuel is delivered to fuel injector 66 by fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Alternatively, the engine may be configured such that the fuel isinjected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection (where the injector is coupled tothe combustion chamber 30). Intake manifold 44 is shown communicatingwith electronic throttle 125, throttle position is based, in part, on asignal from accelerator pedal 119. Alternatively, a mechanical throttleand pedal can be substituted for electronic throttle 125. Air masssensor 38 is located upstream of electronic throttle 125 and provides asignal representative of inducted air mass to controller 12.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to controller 12. Two-stateexhaust gas oxygen sensor 76 is shown coupled to exhaust manifold 48upstream of catalytic converter 70. Alternatively, a Universal ExhaustGas Oxygen (UEGO) sensor may be substituted for two-state sensor 76.Two-state exhaust gas oxygen sensor 98 is shown coupled to exhaust pipe78 downstream of catalytic converter 70. Alternatively, sensor 98 canalso be a UEGO sensor. Catalytic converter temperature is measured bytemperature sensor 77, and/or estimated based on operating conditionssuch as engine speed, load, air temperature, engine temperature, and/orairflow, or combinations thereof.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only memory 106, random-access memory 108, keep-alive memory 110,and a conventional data bus. Controller 12 is shown receiving varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofmanifold absolute pressure (MAP) from pressure sensor 122 coupled tointake manifold 44; a measurement of driver demand from pedal positionsensor 119; a measurement (ACT) of engine air amount temperature ormanifold temperature from temperature sensor 117; and a profile ignitionpickup signal (PIP) from a Hall effect sensor 118 coupled to acrankshaft 40.

Referring to FIG. 2, a schematic diagram that shows an exampleelectrically actuated valve that is being held in an open position, suchas an electromechanical valve. Valve position is measured using linearvariable displacement transducer 200. The position of valve 212 altersthe magnetic flux in the sensor to provide a linear output that isindicative of valve position. Alternatively, other types of analogsensors may be used or discrete sensors can be used to detect valveposition.

Valve position is determined by valve springs 208 and 210 along with thestate of coils 202 and 206. When the coils are not energized, valve 212is held in a mid position by opposing forces that are applied toarmature 204 from springs 208 and 210.

The figure shows coil 206 in an energized state; a magnetic fieldproduced by energizing the coil draws the armature 204 to the coil. Thevalve can be closed by de-energizing coil 206 and energizing coil 202.During the transition from open to closed, spring 210 helps to drive andaccelerate armature 204 from coil 206 to coil 202. Conversely, spring208 helps to drive the armature to coil 206 when the valve is opened.

Referring to FIG. 3, an example flow diagram of an ignition voltagelimiting strategy is shown. In step 302, the strategy determines ifthere is an error in a valve trajectory. In one example, the currentvalve position is compared to a predetermined map that relates valveposition to a crankshaft position. If a valve is off trajectory by athreshold amount, the routine continues to step 304, if not, the routineexits. Each valve that may be held in a position during a cycle of acylinder, (e.g., open or closed), may be evaluated to determine ifignition voltage should be limited in a cylinder based on theoff-trajectory valve. The threshold amount may be adjusted depending onoperating conditions, since more error may be expected under someconditions compared to others, such as, for example: during cold or warmoperating temperatures.

Alternatively, a valve trajectory error may be inferred from otherengine sensors and/or calculations, pressure sensors, flow sensors,temperature sensors, engine position sensors, calculated engineacceleration, and oxygen sensors, and/or combinations thereof, forexample. If valve degradation has occurred, the sensor may provide asignal that can be compared to a nominal reference signal to determinevalve degradation. For example, an engine operating at a given speed andload may usually operate at an air-fuel ratio that is near astoichiometric value. If valve degradation has occurred, an oxygensensor in the exhaust system may observe an exhaust mixture thatdeviates from stoichiometric combustion. Therefore, a determination ofvalve degradation may be determined from an oxygen sensor, based on adeviation from stoichiometry.

In step 304, fuel injection is deactivated to stop fuel flow to thecylinder having an off-trajectory valve. Fuel may be deactivated beforeor during an injection event depending on when valve degradation isdetermined. For example, if a fuel injection interval is scheduled tooverlap the transition from a closed intake valve to an open intakevalve, and an intake valve trajectory error is determined, fuel flow maybe stopped subsequent to the determination of the trajectory error butprior to the end of the scheduled injection interval. On the other hand,if an exhaust valve trajectory error is determined before fuel injectionbegins, fuel injection may be stopped without beginning the injectionevent. The routine proceeds to step 306.

In step 306, ignition coil voltage is limited. Ignition coil voltage canbe generated by any one of several known methods that transformelectrical system voltage into a higher voltage that is capable ofcreating a spark across a spark plug gap. Typical ignition coil circuitconfigurations include B+ common, common ground, and variants.

The B+ common configuration supplies one side of the primary coil andone side of the secondary coil with vehicle electrical system voltage,B+ for example. The primary coil can be charged when current is allowedto flow between B+ and ground. The opposite side of the secondary coilis electrically connected to a spark plug, 92 of FIG. 1 for example. Aspark can be generated at the spark plug by interrupting current flow tothe primary coil when sufficient energy has been stored in the ignitioncoil core.

The common ground configuration supplies the primary coil with B+ anddoes not supply B+ voltage to the secondary coil. One side of thesecondary coil is electrically connected to the spark plug while theopposite end of the coil is electrically connected to ground. A sparkcan be generated at the spark plug by interrupting current flow to theprimary coil after sufficient energy has been stored in the ignitioncoil core.

The above mentioned ignition configurations and known variants can bedesigned to reduce the probability of spark during valve degradation bythe circuits shown in FIGS. 5–10 and variants thereof. As such, theillustrations are not meant to limit the breadth or scope of thedisclosure.

Continuing with step 306, a circuit that can limit ignition coil voltageis electrically coupled to the ignition coil. The coupling may includeelectrical coupling, physical coupling, magnetic coupling, or othercoupling that links the circuits. Ignition coil voltage may be limitedin the primary or secondary coil, but because of higher secondaryvoltages, limiting the primary voltage may be more advantageous in somecases. Ignition voltage can be limited in the affected cylinder untilvalves are on a desired trajectory. The routine then proceeds to step308.

In step 308, on-trajectory valves are set to a predetermined position.If either an intake or an exhaust has been determined to beoff-trajectory, the remaining selectively controllable valves in thecylinder may be set to a closed position until the off-trajectory valveresumes a desired trajectory. If fuel injection has occurred and anair-fuel mixture has been inducted into the cylinder, closingon-trajectory valves may reduce the amount of uncombusted fuel that isexpelled into the exhaust system. Alternatively, on-trajectory intakevalves may be set to an open position for at least one piston strokethat is in the direction of the cylinder head. This may reduce theamount of uncombusted hydrocarbons that may be pumped into the exhaustsystem. Furthermore, open intake valves may allow the air-fuel mixtureto be pumped into the intake manifold where it can be subsequentlycombusted in another cylinder, thereby reducing the chance of combustingin cylinders with off-trajectory valves. The routine continues to step310.

In step 310, an attempt is made to restart the off-trajectory valve. Asdescribed above, electrically actuated valves, and electromechanicalvalves in particular, may assume a center or mid position if they areoff-trajectory. This type of valve may be restarted to resume a desiredtrajectory by directly pulling the valve armature toward an opening orclosing coil, or by oscillating the valve between the opening coil andthe closing coil until the valve can be captured in an open or closedposition. On the other hand, cam driven mechanically operated valves maybe reactivated by making attempts to engage or disengage mechanicaloperating mechanisms. If attempts to restart off-trajectory valve areunsuccessful the cylinder may be deactivated by inhibiting fuel andignition coil current. Alternatively, step 310 may be an externalroutine that is executed at a rate different than the routine of FIG. 3.The routine proceeds to exit.

Referring to FIG. 4, an example flow diagram of an alternate ignitioncoil voltage limiting strategy is shown. In step 402, the strategydetermines if there is an error in a valve trajectory. The method ofFIG. 3, step 302, described above, may be used to determine if a valveis off-trajectory. The routine continues to step 404.

In step 404, the routine determines if the ignition coil has begun tocharge. If current has started to flow into the coil, the routineproceeds to step 410, if not, the routine continues to step 406.

In step 410, ignition coil voltage is limited. The method of FIG. 3,step 306, described above, may be used to limit ignition coil voltage instep 410. After limiting coil voltage the routine proceeds to step 408.

In step 406, ignition coil charging is commanded off. During low speedengine operation or while valve timing is advanced, intake and/orexhaust valve degradation may be determined for a cylinder before a coilbegins to charge. Typical spark dwell (coil charging) times can rangebetween 1–4 milliseconds, at low engine speeds intake valve opening andexhaust valve closing may occur well before an ignition coil begins tocharge. If there is sufficient time between an indication of valvedegradation and starting the flow of ignition coil current, it may bepossible to stop ignition coil current before coil charging starts bycommanding the coil current driving circuit off. The routine proceeds tostep 408.

In step 408, fuel injection is deactivated in the cylinder that hasvalve degradation. As described above, for the description of step 304,fuel may be deactivated before or during an injection event depending onwhen valve degradation is determined and when fuel injection isscheduled. The routine proceeds to step 412.

In step 412, valves that are on-trajectory are set to predeterminedpositions. The method described for step 308 of FIG. 3 may be used toposition on-trajectory valves if one or more valves in a cylinder areoff trajectory. The routine continues to step 310.

In step 414, an attempt to restart the off-trajectory valve is made.That is, an attempt is made to bring the off-trajectory valve back ontrajectory. Specifically, the method described for step 310 of FIG. 3may be used in an attempt to restart the off-trajectory valve. If theattempt to restart the valve is unsuccessful, the cylinder may bedeactivated by stopping fuel flow, air flow, and spark to the cylinder.The routine proceeds to exit.

Referring to FIG. 5, a schematic of an example ignition coil voltagelimiting circuit is shown. The ignition coil is comprised of a primarycoil 500 and a secondary coil 502. Primary coil 500 can be charged byallowing current to flow from low voltage at lead 512 to the low voltagereturn (e.g., ground). Current flow through the primary coil 500 may becontrolled via switch 504 which is connected between the low voltageside of primary coil 500 and low voltage return. Zener diode 508 is alsoconnected to the low voltage side of primary coil 500 and may limitvoltage in primary coil 500 when switch 506 electrically couples zenerdiode 508 between the low voltage side of primary coil 500 and the lowvoltage return.

The switches shown in FIG. 5–10 may be constructed in a variety of waysdepending on the circuit configuration and control objectives. In oneexample, an insulated gate bipolar transistor (IGBT) may be used tocontrol the circuitry. As such, the switch illustrations are not meantto limit the breadth or scope of the disclosure.

When valve degradation has not been determined, ignition spark can becontrolled by an ignition controller that switches switch 504. Whenprimary coil 500 charging is stopped (e.g., by removing current from theprimary coil over a short time period by switch 504) the magnetic fieldin the core can no longer be supported by current in the primary coil.This can cause the magnetic field to rapidly reduce, thereby inducing avoltage in the secondary coil and a spark at the spark plug gap. Theinduced voltage in the secondary coil, created by this decreasingmagnetic field, can be higher than the voltage in the primary coil ifthere are a greater number of turns in the secondary coil, relative tothe primary coil.

If valve degradation has been determined, the low voltage side of theprimary ignition coil can be electrically coupled to the low voltagereturn through an electrical network comprising zener diode 508 (othercomponents may be substituted for the zener diode, a metal oxidevaristor for example). Switch 506 can be controlled to electricallycouple the network to primary coil 500 during an indication of valvedegradation. When the electrical network is coupled to primary coil 500,zener diode 508 does not conduct in the in the forward direction becausethe low voltage return is at a lower potential than the low voltage sideof primary coil 500. However, current can flow through zener diode 508in the reverse direction if the diode breakdown voltage is exceeded. Thebreakdown voltage can be exceeded if there is energy stored in ignitioncoil core, and if current flow into primary coil 500 is quickly stopped.Therefore, if an ignition controller is switching switch 504, and ifzener diode 508 and switch 506 are coupled to primary coil 500, thezener diode can limit the voltage at the low voltage side of primarycoil 500 by allowing current to flow to the low voltage return. In thisway, the energy stored in primary coil 500 can be extracted at acontrolled rate so that the induced voltage of secondary coil 502remains low enough to reduce the possibility of a spark at spark pluggap 510, thereby interrupting a spark event.

When the low voltage side of the primary coil is de-coupled from the lowvoltage return, zener diode 508 does not conduct so that the primaryvoltage may not be limited by the electrical network (switch 506 andzener diode 508).

Referring to FIG. 6, a schematic of another example ignition coilvoltage limiting circuit is shown. Again, an ignition coil is comprisedof a primary coil 600 and a secondary coil 602. Primary coil 600 can becharged by allowing current to flow from low voltage at lead 612 to thelow voltage return (e.g., ground). Current flow through the primary coil600 may be controlled via switch 606 which is connected between the lowvoltage side of primary coil 600 and low voltage return. Zener diode 608is also connected to the low side of primary coil 600 and may limitvoltage in primary coil 600 when switch 604 electrically couples zenerdiode 608 between the low voltage side of primary coil 600 and the lowvoltage supply 612.

When valve degradation has not been determined, ignition spark can becontrolled by an ignition controller that switches switch 606. Theignition coil can be used to create ignition spark in a manner as isdetailed in the description of FIG. 5.

If valve degradation has been determined, the low voltage input side ofthe primary ignition coil 600 can be electrically coupled to the lowvoltage return side of primary coil 600 through an electrical networkcomprising zener diode 608 (again, other components may be substitutedfor the zener diode, a metal oxide varistor for example). Switch 604 canbe controlled to limit voltage in primary coil 600 by allowing zenerdiode 608 to conduct in the reverse direction (from the low voltage sideof the primary coil to the high side of the primary coil) if thebreakdown voltage is exceeded. Switch 604 should be controlled such thatzener diode 608 is coupled to primary coil 600 just before current flowis stopped between primary coil 600 and the low voltage return. Couplingzener diode 608 to primary coil 600 just before current flow is stopped,can limit the forward current flow from low voltage source 612 throughzener diode 608 to low voltage return.

Referring to FIG. 7, a schematic of an ignition coil comprising aprimary coil 700, core, secondary coil 702, and an auxiliary coil 704 isshown. A low voltage is supplied to one side of the primary coil whilethe other side of the primary coil can be connected to the low voltagereturn through switch 706. Secondary coil 702 has one side connected tolow voltage supply 712 while the opposite side of the coil is connectedto a spark plug. One side of auxiliary coil 704 is connected to lowvoltage supply 712 while the opposite side of the coil can be connectedto low voltage return, via switch 708. The auxiliary coil can be woundwith polarity that is the reverse of the primary coil.

When valve degradation is not determined, primary coil 700 can storeenergy in the ignition coil core while switch 706 allows current to flowfrom low voltage supply 712 to the low voltage return. When the ignitioncoil core has stored sufficient energy, a spark can be generated atspark plug gap 710 by quickly stopping current from low voltage supply712.

If valve degradation is determined, the secondary coil voltage can belimited by maintaining the magnetic flux by flowing current throughauxiliary coil 704 and switch 708. The current in the auxiliary coil canthen be decreased at a rate that reduces the possibility of creating aspark from the voltage induced at the secondary coil.

Referring to FIG. 8, a schematic of an alternate ignition coil havingprimary coil 800, core, secondary coil 802, and auxiliary coil 804 isshown. A low voltage supply 812 is connected to one side of the primarycoil while the other side of the primary coil is connected to one sideof the auxiliary coil. The primary coil can also be connected to the lowvoltage return through switch 806. Secondary coil 802 has one sideconnected to low voltage supply 812 while the opposite side of the coilis connected to a spark plug. One side of auxiliary coil 804 isconnected to the low voltage side of the primary coil while the oppositeside of the coil can be connected to the low voltage side of the primarycoil, via switch 808.

When valve degradation is not determined, primary coil 800 can storeenergy in the core while switch 806 allows current to flow from lowvoltage supply 812 to the low voltage return. When the core has storedsufficient energy, a spark can be generated at spark plug gap 810 byquickly stopping current from low voltage supply 812.

If valve degradation is determined, switch 808 can shunt auxiliary coil804. By shunting the coil, a low impedance path may be provided todissipate the energy stored in the ignition coil core when current flowis interrupted to the primary coil. Consequently, current can bepreferentially induced in the auxiliary coil over the secondary coil.This can reduce the possibility of creating a spark at the spark plug.

Referring to FIG. 9, a schematic of an alternate ignition coil having aprimary coil 900, secondary coil 902, core, and an auxiliary coil 904 isshown. The one side of the primary coil is connected to low voltagesupply 912 while the opposite side can be connected to low voltagereturn via switch 906. The secondary coil is connected to low voltagesupply 912 and a spark plug. The auxiliary coil leads may be connectedtogether (shunted) through switch 908. The auxiliary coil can be woundwith polarity that is the reverse of the primary coil.

When valve degradation is not determined, primary coil 900 can storeenergy in the core while switch 906 allows current to flow from lowvoltage supply 912 to the low voltage return. When there is sufficientenergy stored in the core, a spark can be generated at spark plug gap910 by quickly stopping current flow from low voltage supply 912.

If valve degradation is determined, switch 808 can shunt auxiliary coil904. By shunting the coil, a low impedance path may be provided todissipate the energy stored in the ignition coil core when current flowis interrupted to the primary coil. Consequently, current can bepreferentially induced in the auxiliary coil over the secondary coil.This can reduce the possibility of creating a spark at the spark plug.Operation of this circuit is essentially equivalent to that detailed inthe description of FIG. 8.

Referring to FIG. 10, a schematic of an alternate ignition coil having aprimary coil 1000, secondary coil 1002, core, and an auxiliary coil 1004is shown. A low voltage supply 1012 is connected to one side of theprimary coil while the opposite side of the primary coil can beconnected to the low voltage return through switch 1008. Secondary coil1002 has one side connected to low voltage supply 1012 while theopposite coil side is connected to a spark plug. One side of auxiliarycoil 1004 is connected to low voltage return while the opposite side canbe connected to low voltage supply 1012, via switch 1006.

Operation of the circuit shown is FIG. 10 is similar to circuitoperation detailed in the description of FIG. 7. Switch 1006 can becontrolled to allow current flow into auxiliary coil 1004, therebysupporting the magnetic flux generated by the primary coil 1000. Thelocation of the auxiliary coil switching switch may be preferred when asshown in FIG. 7, or alternatively, as shown in FIG. 10.

Referring to FIG. 11, a plot of simulated ignition coil voltagelimitation is shown. In particular, energy flow to the primary coil isreduced by yet another voltage limiting arrangement, where a resistor isswitched into the primary coil circuit, such that it is connected inparallel to the primary coil. In the figure, current is interrupted tothe primary coil at approximately 4 ms and 28 ms. When the spark inhibitsignal is low (before 20 ms), interrupting current flow to the primarycoil can cause an increase in the secondary coil voltage that may resultin a spark at the spark plug. When the spark inhibit signal is high(after 20 ms), the secondary voltage is limited to less than a fewhundred volts, reducing the possibility of spark at the spark plug.

As will be appreciated by one of ordinary skill in the art, the routinesdescribed in FIGS. 3 and 4 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, or alternative fuel configurations could use the presentdescription to advantage.

1. A method of interrupting at least a spark event to at least acylinder of a multi-cylinder internal combustion engine having at leasta valve operable in the cylinder, the method comprising: limiting thevoltage of an ignition coil after beginning to charge said ignitioncoil; and said voltage limited while reducing the possibility ofproducing a spark at a spark plug coupled to said ignition coil.
 2. Themethod of claim 1 wherein said ignition coil has a primary winding, asecondary winding, and a core.
 3. The method of claim 2 wherein saidvoltage is limited in said primary winding.
 4. The method of claim 1wherein said valve is an electrically actuated valve.
 5. The method ofclaim 4 wherein said electrically actuated valve is an electromechanicalvalve.
 6. The method of claim 2 wherein said limiting the voltage isachieved by reducing the electrical energy of said primary winding afteran indication of valve degradation.
 7. The method of claim 2 whereinsaid limiting the voltage is accomplished by reducing the magneticenergy of said core that is inducing a voltage in said secondary windingafter an indication of valve degradation.
 8. The method of claim 1wherein the operation of said valve may be adjusted to alter the lift ortiming of said valve.
 9. The method of claim 1 wherein said valve is anintake valve.
 10. The method of claim 1 wherein said valve is an exhaustvalve.
 11. The method of claim 1 wherein said spark plug is located in acylinder and further comprising deactivating fuel flow to said cylinderwhen said voltage is limited.
 12. A method of interrupting at least aspark event to at least a cylinder of a multi-cylinder internalcombustion engine having at least a valve operable in the cylinder, themethod comprising: limiting the voltage of an ignition coil afterbeginning to charge said ignition coil; said voltage limited whilereducing the possibility of producing a spark at a spark plug coupled tosaid ignition coil; and limiting said voltage after an indication thatthe operation of said valve has degraded.
 13. The method of claim 12wherein said spark plug is located in a cylinder and further comprisingdeactivating fuel flow to said cylinder when said voltage limited. 14.The method of claim 12 wherein the operation of said valve may beadjusted to alter the lift or timing of said valve.
 15. The method ofclaim 12 wherein said valve is an exhaust valve or an intake valve. 16.A method of interrupting at least a spark event to at least a cylinderof a multi-cylinder internal combustion engine having at least a valveoperable in the cylinder, the method comprising: limiting the voltage ofan ignition coil after beginning to charge said ignition coil; saidvoltage limited while reducing the possibility of producing a spark at aspark plug coupled to said ignition coil; and positioning valves in acylinder while said voltage is limited.
 17. The method of claim 16wherein said valve is in the same cylinder as said spark plug.
 18. Themethod of claim 16 wherein said valve is an electrically actuated valve.19. The method of claim 16 wherein said voltage is limited in responseto degradation of a valve in said cylinder.
 20. The method of claim 16wherein said positioning closes said valves.